The purposes of this project are: (1) to compare patterns of impairment in language and communicative functions, psychiatric, and neurologic status in Parkinson's disease (PD) and Alzheimer's disease (AD); (2) to describe the progression of change in language and communicative functions, psychiatric, and neurologic status during the course of PD and AD; and (3) to determine the relation of onset and duration of symptoms and depression in PD and AD to the nature of language and communication deficits. One hundred PD patients (subclassified as to presence or absence of dementia), 50 AD patients (25 with extrapyramidal symptomatology and 25 without), and 50 normal elderly individuals (25 young-old and 25 older-old) matched for age, sex, education, race, and intelligence to the PD and AD patient groups will participate in the study. The investigators have chosen to approach the study of the effects of PD and AD on language and communicative function as an investigation of semantic, episodic, and procedural memory because deficits in the different communicative functions are reducible to deficits in these more generic systems. Prior to the administration of a comprehensive battery of the semantic, episodic, and procedural memory tasks, all subjects will receive a neurologic and physical examination, be rated on the Hoehn and Yahr, Columbia, and Northwestern Clinical Scales, and have their drug regimen specified and evaluated. Thereafter they will be interviewed and evaluated for depression using the Diagnostic Interview Schedule and Hamilton Rating Scale. The presence of dementia will be established using the DSM-III criteria, the Mattis Dementia Scale and the Global Deterioration Scale. The performance of PD patients on the semantic, episodic, and procedural memory tasks will be evaluated during the period of optimal drug effect, a regimen that will require two days. AD patients and normal elderly subjects will be evaluated over the course of one day. PD patients who have not received drug therapy will be evaluated before drug treatment and at three and six month intervals after the initiation of drug therapy to assess drug effects on test performance. With the exception of this subject of PD patients, study participants will be tested twice during the five year project duration. Data analysis, employing factor analysis for data reduction, will rely primarily upon multivariate analyses of variance for hypothesis testing. A series of specific hypotheses, concerned with dissociations between the different memory domains in AD versus PD patient groups, and with neurologic and psychiatric correlates of differential patterns and courses of communicative impairment, will be tested.